Stanley A. Leake

A New Capture Fraction Method to Map How Pumpage Affects Surface Water Flow

All groundwater pumped is balanced by removal of water somewhere, initially from storage in the aquifer and later from capture in the form of increase in recharge and decrease in discharge. Capture that results in a loss of water in streams, rivers, and wetlands now is a concern in many parts of the United States. Hydrologists commonly use analytical and numerical approaches to study temporal variations in sources of water to wells for select points of interest. Much can be learned about coupled surface/groundwater systems, however, by looking at the spatial distribution of theoretical capture for select times of interest. Development of maps of capture requires (1) a reasonably well-constructed transient or steady state model of an aquifer with head-dependent flow boundaries representing surface water features or evapotranspiration and (2) an automated procedure to run the model repeatedly and extract results, each time with a well in a different location. This paper presents new methods for simulating and mapping capture using three-dimensional groundwater flow models and presents examples from Arizona, Oregon, and Michigan.

Review: groundwater in Alaska (USA)

Groundwater in the US state of Alaska is critical to both humans and ecosystems. Interactions among physiography, ecology, geology, and current and past climate have largely determined the location and properties of aquifers as well as the timing and magnitude of fluxes to, from, and within the groundwater system. The climate ranges from maritime in the southern portion of the state to continental in the Interior, and arctic on the North Slope. During the Quaternary period, topography and rock type have combined with glacial and periglacial processes to develop the unconsolidated alluvial aquifers of Alaska and have resulted in highly heterogeneous hydrofacies. In addition, the long persistence of frozen ground, whether seasonal or permanent, greatly affects the distribution of aquifer recharge and discharge. Because of high runoff, a high proportion of groundwater use, and highly variable permeability controlled in part by permafrost and seasonally frozen ground, understanding groundwater/surface-water interactions and the effects of climate change is critical for understanding groundwater availability and the movement of natural and anthropogenic contaminants.RésuméL’eau souterraine dans l’état américain d’Alaska est essentielle à la fois pour les humains et pour les écosystèmes. Les interactions entre physiographie, écologie, géologie, climat passé et actuel, ont largement déterminé la localisation et les caractéristiques des aquifères comme d’ailleurs le rythme et l’amplitude des flux entrants, sortants et internes au système aquifère. Le climat s’échelonne du maritime dans la partie Sud au continental dans l’intérieur à l’arctique sur le Versant Nord. Durant l’ère quaternaire, topographie et nature des roches se sont combinées avec les mécanismes glaciaires et péri-glaciaires pour former les aquifères alluviaux non consolidés d’Alaska, d’où ont résulté des hydrofaciès extrêmement hétérogènes. De plus, la longue persistance d’un sol gelé, soit saisonnier soit permanent, affecte grandement la distribution de la recharge et de la décharge des aquifères. En raison d’une forte utilisation de l’eau de surface et de l ‘eau souterraine, et d’une perméabilité de la nappe hautement variable, contrôlée en partie par le permafrost et par le gel saisonnier, comprendre les interactions eau souterraine-eau de surface ainsi que les effets du changement climatique est crucial pour l’appréhension de la disponibilité en eau souterraine et du transfert des polluants naturels et anthropiques.ResumenEl agua subterránea en el estado de Alaska es crítica para los seres humanos y los ecosistemas. Las interacciones entre la fisiografía, ecología, geología y el clima actual y pasado han determinado en gran parte la ubicación y las propiedades de los flujos, así como el tiempo y magnitud de flujos hacia, desde y dentro del sistema de agua subterránea. El clima varía desde marítimo en la porción sur del estado a continental en el interior, y ártico en la ladera norte. Durante el período Cuaternario, la topografía y el tipo de roca se ha combinado con procesos glaciales y periglaciales para desarrollar los acuíferos aluviales no consolidados de Alaska y ha resultado en hidrofacies altamente heterogéneas. Además, la gran persistencia del terreno congelado, ya sea estacional o permanente, afecta en gran medida la distribución de la recarga y descarga del acuífero. Debido al alto escurrimiento y el uso del agua subterránea, y la permeabilidad altamente variable controlada en parte por el permafrost y estacionalmente por el terreno congelado, la comprensión de la interacción superficial – agua subterránea y los efectos del cambio climático es critico para el conocimiento de la disponibilidad de agua subterránea y los movimientos de contaminantes naturales y antropogénicos.摘要美国阿拉斯加州的地下水资源对于人类和生态系统都是至关重要的。自然地理条件、生态环境、地质条件和古往今来的气候条件之间的相互作用在很大程度上决定了含水层的位置和特性, 以及流入、流出和存在于地下水系统中的水流的流动时间和规模。州内的气候条件变化很大, 由南向北, 南部为海洋性气候, 中部为大陆性气候, 阿拉斯加北坡为北极气候。在第四纪期间, 地形和岩石的类型与冰期、间冰期过程相结合, 形成了阿拉斯加松散的冲积含水层, 导致了水相的高度非均质化。除此之外, 长期呈冷冻状态的土壤, 无论是季节性的还是永久性的, 都极大地影响了含水层源汇区的分布。由于径流量、地下水使用量很大, 且部分受永久性、季节性冻土控制的渗透性是高度变化的, 弄清地下水-地表水的相互作用和气候变化对其的影响, 对于了解地下水的可用性和自然、人为污染物的运移是非常重要的。ResumoA água subterrânea no estado norte-americano do Alasca é fundamental para os seres humanos e para os ecossistemas. Interações entre a fisiografia, a ecologia, a geologia e o clima atual e passado determinaram largamente a localização e as propriedades dos aquíferos bem como a temporização e a magnitude dos fluxos de, para e dentro do sistema de águas subterrâneas. O clima varia de marítimo na parcela sul do estado a continental no interior, e a ártico na Encosta Norte. Durante o período Quaternário, a topografia e o tipo de rochas combinaram-se com os processos glaciar e periglacial para desenvolver os aquíferos aluvionares não consolidados do Alasca, resultando em hidrofácies altamente heterogéneas. Além disso, o congelamento persistente do solo, seja sazonal ou permanente, afeta extremamente a distribuição da recarga e da descarga dos aquíferos. Devido ao elevado escoamento superficial e do uso da água subterrânea, e da variabilidade elevada da permeabilidade, controlada em parte pelo permafrost e pelo solo sazonalmente congelado, a compreensão das interações água subterrânea/água superficial e dos efeitos das mudanças climáticas é crítica para o conhecimento da disponibilidade de água subterrânea e do movimento de contaminantes naturais e antropogénicos.

Feedback of land subsidence on the movement and conjunctive use of water resources

The dependency of surface- or groundwater flows and aquifer hydraulic properties on dewatering-induced layer deformation is not available in the USGSs groundwater model MODFLOW. A new integrated hydrologic model, MODFLOW-OWHM, formulates this dependency by coupling mesh deformation with aquifer transmissivity and storage and by linking land subsidence/uplift with deformation-dependent flows that also depend on aquifer head and other flow terms. In a test example, flows most affected were stream seepage and evapotranspiration from groundwater (ETgw). Deformation feedback also had an indirect effect on conjunctive surface- and groundwater use components: Changed stream seepage and streamflows influenced surface-water deliveries and returnflows. Changed ETgw affected irrigation demand, which jointly with altered surface-water supplies resulted in changed supplemental groundwater requirements and pumping and changed return runoff. This modeling feature will improve the impact assessment of dewatering-induced land subsidence/uplift (following irrigation pumping or coal-seam gas extraction) on surface receptors, inter-basin transfers, and surface-infrastructure integrity. We develop a method to simulate deformation-dependent flows for MODFLOW.We demonstrate the significance of linking subsidence to conjunctive water use.The linkages affect flows across the landscape, surface water, and groundwater.Linked flows are relevant to resource issues that include conjunctive water use.

Capture Versus Capture Zones: Clarifying Terminology Related to Sources of Water to Wells: P.M. Barlow et al. Groundwater XX, no. X: XX-XX

The term capture, related to the source of water derived from wells, has been used in two distinct yet related contexts by the hydrologic community. The first is a water-budget context, in which capture refers to decreases in the rates of groundwater outflow and (or) increases in the rates of recharge along head-dependent boundaries of an aquifer in response to pumping. The second is a transport context, in which capture zone refers to the specific flowpaths that define the three-dimensional, volumetric portion of a groundwater flow field that discharges to a well. A closely related issue that has become associated with the source of water to wells is streamflow depletion, which refers to the reduction in streamflow caused by pumping, and is a type of capture. Rates of capture and streamflow depletion are calculated by use of water-budget analyses, most often with groundwater-flow models. Transport models, particularly particle-tracking methods, are used to determine capture zones to wells. In general, however, transport methods are not useful for quantifying actual or potential streamflow depletion or other types of capture along aquifer boundaries. To clarify the sometimes subtle differences among these terms, we describe the processes and relations among capture, capture zones, and streamflow depletion, and provide proposed terminology to distinguish among them.

The Effect of modeled recharge distribution on simulated groundwater availability and capture

Simulating groundwater flow in basin-fill aquifers of the semiarid southwestern United States commonly requires decisions about how to distribute aquifer recharge. Precipitation can recharge basin-fill aquifers by direct infiltration and transport through faults and fractures in the high-elevation areas, by flowing overland through high-elevation areas to infiltrate at basin-fill margins along mountain fronts, by flowing overland to infiltrate along ephemeral channels that often traverse basins in the area, or by some combination of these processes. The importance of accurately simulating recharge distributions is a current topic of discussion among hydrologists and water managers in the region, but no comparative study has been performed to analyze the effects of different recharge distributions on groundwater simulations. This study investigates the importance of the distribution of aquifer recharge in simulating regional groundwater flow in basin-fill aquifers by calibrating a groundwater-flow model to four different recharge distributions, all with the same total amount of recharge. Similarities are seen in results from steady-state models for optimized hydraulic conductivity values, fit of simulated to observed hydraulic heads, and composite scaled sensitivities of conductivity parameter zones. Transient simulations with hypothetical storage properties and pumping rates produce similar capture rates and storage change results, but differences are noted in the rate of drawdown at some well locations owing to the differences in optimized hydraulic conductivity. Depending on whether the purpose of the groundwater model is to simulate changes in groundwater levels or changes in storage and capture, the distribution of aquifer recharge may or may not be of primary importance.

NEW GHOST-NODE METHOD FOR LINKING DIFFERENT MODELS WITH VARIED GRID REFINEMENT

A flexible, robust method for linking grids of locally refined models that may be constructed using different types of numerical methods is needed to address a variety of hydrologic problems. This work outlines and tests a new ghost-node model-linking method based on the iterative method of Mehl and Hill (2002, 2004). It is applicable to steady-state solutions for ground-water flow. Tests are presented for a homogeneous two-dimensional system that facilitates clear analysis of typical problems. The coupled grids are simulated using the finite-difference and finite-element models MODFLOW and FEHM. Results indicate that when the grids are matched spatially so that nodes and control volume boundaries are aligned, the new coupling technique has approximately twice the error as coupling using two MODFLOW models. When the grids are non-matching; model accuracy is slightly increased over matching grid cases. Overall, results indicate that the ghost-node technique is a viable means to accurately couple distinct models.

U.S. Geological Survey Subsidence Interest Group Conference, Proceedings of the Technical Meeting, Las Vegas, Nevada, February 14-16, 1995

Abstract : Land subsidence is the loss of surface elevation as a result of the removal of subsurface support. The mechanisms by which this can occur may be natural in origin or induced by human activities. Common causes of land subsidence include the removal of oil, gas, and water from underground reservoirs; dissolution of limestone aquifers (sinkholes); underground mining activities; drainage of organic soils; and hydrocompaction (the initial wetting of dry soils). Overdraft of aquifers is the major cause of a really extensive land subsidence, and as ground-water pumping increases, land subsidence also will increase. The U.S. Geological Survey (USGS) has a long-standing history of describing, mapping, and conducting process-oriented research in land subsidence. In 1955, the Geological Survey formed the Mechanics of Aquifers Project under the direction of Joseph F. Poland to study the processes that result in land subsidence due to the withdrawal of ground water. From 1955 to 1984, this research team gained international renown as they advanced the understanding of aquifer mechanics and land-subsidence theory. In addition to conducting pioneering research, this group also provided a focal point within the USGS for the dissemination of technology and scientific understanding in aquifer mechanics.